1. Field of The Invention
The present invention relates to an apparatus for vibration damping, and more particularly to a viscous damper having a compact folded structure for space satellite applications.
2. Description of The Prior Art
Spacecraft applications have shown an increasing need for vibration isolation. Such applications include the reduction of emitted vibrations from dynamically operating hardware such as rotating machinery, and to protect sensitive hardware from launch vibration and spacecraft disturbances. A structure which provided broad band isolation at very low disturbance levels was described in the L. P. Davis U.S. Pat. No. 4,760,996, assigned to the assignee of the present invention, which employed metal springs acting in parallel with a viscous fluid damping element. Stiffness was provided by coil springs operating in parallel with a metal bellows. Damping is provided by viscous flow of a damping fluid through an annular damping chamber during payload motion. However, this structure required a substantial length as it required a stacked array of bellows topped by a thermal compensator to correct for expansion and contraction of the damping fluid with temperature changes. A further drawback of the prior art structure was that it required a longitudinal rod packaged within the bellows to maintain a constant total volume, so that as one bellows was caused to expand, the other bellows was caused to contract. This required that sufficient height be provided for longitudinally aligning the first and second bellows and the thermal compensator. Since the total volume was maintained constant, it was necessary to provide the auxiliary thermal compensator to allow for expansion of the damping fluid with temperature.
Advantageously, it has been discovered that a structure which allows the primary and secondary bellows to expand or contract substantially independently with temperature changes in the damping fluid will allow a more compact design to be obtained by "folding" the structure and obviates the need for the volumetric confining shaft and thermal compensator. The present invention provides flexibility in design so that it can be used to provide a multi-axis damper or isolation system in a small size, hermetically sealed package without being subject to Coulomb forces and wearing of frictional surfaces. It provides linear performance and large damping values over a large dynamic range, including small vibration perturbations. The simplified mechanical design permits lower cost fabrication as compared to the prior art structures.